Bring 8 cups unsalted water to a boil in a 6 to 8 quart pot, then add noodles, stirring to separate, and cook 15 seconds. Drain in a colander and rinse under cold water until noodles are cool, then shake colander briskly to drain excess water.

Cut steak with the grain into 1-1/2 to 2 inch wide strips. Cut each strip across the grain into 1/4 inch thick slices and put in a medium bowl. Using your hands, toss beef with sugar, sesame oil, 1 tablespoon soy sauce, 1 tablespoon rice wine, 1 tablespoon oyster sauce, and 1 teaspoon cornstarch. Let beef marinate at room temperature while preparing remaining ingredients.

Stir together remaining 1 tablespoon soy sauce, 1 tablespoon rice wine, 1 tablespoon oyster sauce, 1 teaspoon cornstarch with 1/4 teaspoon white pepper in a small bowl until smooth, then stir in chicken broth.

Heat wok over high heat until a drop of water evaporates within 1 to 2 seconds of contact, then add 1/2 cup peanut oil and heat until just smoking. Carefully add noodles all at once, flattening top to form a 9 inch cake. Cook until the underside is golden, 4 to 5 minutes, rotating noodle cake with a metal spatula to brown evenly and lifting edges occasionally to check color. Carefully flip noodle cake over with spatula and tongs, then cook, rotating cake, until the other side is golden, 2 to 3 minutes more. Transfer noodle cake to a large paper towel lined plate to drain excess oil. Discard any oil. Transfer drained noodle cake to a platter and loosely cover with foil to keep warm.

Heat wok over high heat until a drop of water evaporates within 1 to 2 seconds of contact, pour 1 tablespoon of peanut oil down side of the wok, then swirl oil, tilting wok to coat sides. Add beef, spreading pieces in 1 layer on bottom and sides as quickly as possible. Cook, undisturbed, letting beef begin to brown, 1 minute, then stir fry untill meat is just browned on all sides but srill pink in the center, about 1 minute, transfer meat and any juices to a plate.

Add 1 tablespoon of oil to wok over high heat. When the oil just begins to smoke, add ginger and garlic and stir fry 5 seconds, then add scallions and stir fry 30 seconds. Add mushrooms and stir fry until softened, about 3 minutes. Add choy sum and stir fry until leaves are bright green and just wilted, 2 to 3 minutes (if using broccoli, cook until almost crisp tender). Stir broth mixture, then pour into wok and stir fry until sauce is slightly thickened, about 2 minutes. Add beef and stir to coat. Return mixture just to a boil, then pour over noodle cake.